Language changes. Culture changes. And we can see some of these changes via what authors write about in books over the years. Google's Book Ngram Viewer lets you search through this data, and shows a graph similar similar to the output of Google Trends. The above is the trends for nursery school, kindergarten, and child care:
This shows trends in three ngrams from 1950 to 2000: "nursery school" (a 2-gram or bigram), "kindergarten" (a 1-gram or unigram), and "child care" (another bigram). What the y-axis shows is this: of all the bigrams contained in our sample of books written in English and published in the United States, what percentage of them are "nursery school" or "child care"? Of all the unigrams, what percentage of them are "kindergarten"? Here, you can see that use of the phrase "child care" started to rise in the late 1960s, overtaking "nursery school" around 1970 and then "kindergarten" around 1973. It peaked shortly after 1990 and has been falling steadily since.
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